Conformational Study of Solid Polypeptides by 1H Combined Rotation and Multiple Pulse Spectroscopy NMR

The relation between the 1 H chemical shift and the conformation of linear homopolypeptides and cyclic dipeptides in the solid state has been studied utilizing the 1 H combined rotation and multiple pulse spectroscopy (CRAMPS) NMR method. It was found that the 1 H chemical shift of the H α signal of homopolypeptides depends on the secondary structure such as α-helix or β-sheet form, whereas those of the side-chain proton signals (H β, H γ, H δ, etc.) are almost independent of the secondary structure. The 1 H chemical shifts of the H α signal of homopolypeptides having the α-helix and the β-sheet forms were 3.9−4.0 ppm and 5.1−5.5 ppm, respectively. Accordingly, the 1 H chemical shift of the H α is very useful for conformational analysis of polypeptides in the solid state. Furthermore, it is shown that the 1 H chemical shift of the H α and the NH signals of cyclic dipeptides are sensitive to the ring conformation and the hydrogen bond length in the solid state.